Temperamental

[Sarah]

Of or pertaining to temperament; constitutional. [R.] Sir T.Browne.

[Sarah]

A person that can explode at any given moment, one minute everything can be super-duper and their company that of something wonderful and the next they are loathsome. They are very volatile and often the hothead. I know this how? I am describing me.

[Sarah]

A half temper and a half mental

[Marquetta]

A temperamental person is someone whose mood often changes very suddenly:

[Tracie Lynn]

(of a person) liable to unreasonable changes of mood.